Preheat oven to 350F and grease a 9-inch cake pan.
In a stand mixer with the paddle attachment, cream together the butter and sugar until mixture becomes light and fluffy. Add in the eggs, one at a time and mix until well-combined. Add vanilla.
In a separate bowl, combine flour, almond flour, baking powder, and salt. Whisk together.
In large measuring cup, combine the ricotta and milk.
Add half the dry ingredients and half of the ingredients in them measuring cup to the butter-sugar mixture. Mix together lightly. Add the remainder of the ingredients and mix until just combined.
Arrange apple slices on top of the batter.
Bake cake for 40 - 45 minutes, until a skewer inserted into the middle comes out clean. If the apples are browning too quickly, place a sheet of foil on top while the cake continues to bake.
Once cake is ready, take the cake out of the oven. Allow cake to cool for 30 minutes before glazing with a pastry brush.